1. Field of the Invention
The present invention relates to powdery crystalline cellulose and a method for preparing the same and more specifically to novel powdery crystalline cellulose having a specific average degree of polymerization and a specific average particle size, and a method for preparing the same.
2. Description of the Prior Art
Recently, foods, cosmetics, medicines as well as various industrial products have been diversified in their applications and they have been required to have high qualities in order to meet the requirements of such application. Therefore, there is big demand that powdery crystalline cellulose to be used in such applications must have a high purity, a high degree of polymerization and a fine particle size.
Up to now, the powdery crystalline cellulose has been conventionally obtained by hydrolyzing, with an acid, a natural cellulose material such as cotton, flax, ramie, jute or hemp, paper or wood; a regenerated cellulose material such as rayon or cuprammonium rayon; or a processed product thereof, to remove its non-crystalline part and then mechanically pulverizing the resultant product, as disclosed in Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J. P. KOKOKU") No. 40-26274.
It is known that cellulose is decomposed by a cellulose derived from mold, bacteria or the like as described in IWANAMI RIKAGAKU JITEN (IWANAMI Physicochemical Dictionary), 3rd ed., 736, issued by IWANAMI BOOK COMPANY.
In such conventional methods for preparing powdery crystalline cellulose, the fiber strength of the cellulose materials should be lowered to facilitate the mechanical pulverization of the cellulose material and to obtain fine powdery crystalline cellulose with a high purity. For this reason, strict conditions are necessary for the hydrolysis with an acid. For instance, the hydrolysis with an acid is carried out at 100.degree. C. for several hours at an acid concentration of 1N when hydrochloric acid is used and at 50.degree. C. for several hours to ten and several hours at an acid concentration of 5N when sulfuric acid is used.
However, the degree of polymerization of the cellulose fibers per se is greatly lowered under such severe hydrolysis conditions and, therefore, it is impossible to obtain physically and chemically stable fine powdery crystalline cellulose having excellent mechanical strength and durability. Therefore, a method for preparing powdery crystalline cellulose having a high degree of polymerization has been strongly demanded to be developed.